Dry scrubbing is a process whereby flue gas is generally injected with a mixture of water, lime, and fly ash in order to reduce the SO.sub.2 content in the flue gas. Other possible reagents (in addition to lime) include limestone, trona (sodium based), and magnesium compounds such as MgCO.sub.3 and MgO. As this process proceeds, CaSO.sub.3.sup..01 /.sub.2 H.sub.2 O and other waste product material (now in dry form) collect, agglomerate, and precipitate out while still being entrained within the flue gas. In some cases, a portion of this dry waste product material is captured, re-mixed with a lime slurry solution, and sprayed back into the scrubber for increased SO.sub.2 removal. There are many designs for such a spray nozzle or atomizer so that the waste product/lime slurry solution is properly mixed and delivered as needed.
As is well known, the key to dry sulfur removal is intimate gas/slurry contact. To achieve optimum contact, control over the preparation and mixing of the waste product/lime slurry solution must be maintained. Subsequent to such contact, however, this slurry solution must be stored afterwhich it must be transported, such as by pumps, through the atomizers into the scrubber. Because of the removal of the waste product from the hot flue gas and its subsequent mixing with the lime slurry, the temperature of the captured waste product decreases dramatically. This encourages agglomeration to occur within the transportation system which can, and most likely will, plug the atomizers. To overcome this, a variety of spray nozzles have been designed with the stated purpose of correcting this deficiency. However, even the best laid plans often go awry because these designs address the symptom of the problem (preventing clogging) rather than the root cause of it (why is there agglomeration in the first place).
It is thus an object of this invention to provide a means of recirculating unreacted reagent back to the scrubber which will not block or plug the injection nozzle. Another object of this invention is to provide a means of recirculating unreacted reagent back to the scrubber which does not require any pre-mixing or spraying with a lime slurry solution. Yet another object of this invention is to provide a means of introducing dry solids back to the scrubber without the need to add water or other liquid to re-slurry this recycled product. Still another object of this invention is to improve reagent utilization by recycling ash (unreacted lime, calcium-sulfur salts, fly ash) in such a manner that less equipment is required thereby resulting in fewer moving parts that can jam, become inoperative, or require maintenance. A further object of this invention is to obviate the need for an ash hopper and an ash removal system, expensive equipment which requires additional energy for operation and occupies valuable space. Still another object of this invention is to facilitate re-entrainment of the recycled ash and the slurry particulates as they fall by gravity within the scrubber. These and other objects and advantages will become obvious upon further consideration.